Koprecipitáció

Koprecipitáció, also known as coprecipitation, is a process in analytical chemistry where an impurity or a valuable substance is precipitated along with a desired compound. This phenomenon occurs when the impurity is present in low concentrations in a solution and forms a solid phase with the main precipitate due to similarities in crystal structure or the formation of solid solutions.

There are several mechanisms by which coprecipitation occurs. Adsorption is common, where ions or molecules from the solution adhere to the surface of the growing precipitate. Occlusion happens when impurities are trapped within the crystal lattice of the precipitate as it forms. Isomorphous substitution takes place when an impurity ion has a similar ionic radius and charge to the ions in the precipitate, allowing it to substitute into the crystal lattice. Finally, mechanical entrapment can occur, where small droplets of the mother liquor containing impurities are enclosed within the precipitate.

Understanding and controlling coprecipitation is crucial for accurate quantitative analysis. If the coprecipitated substance is an impurity, it can lead to overestimation of the desired analyte's mass. Conversely, if the coprecipitated substance is a valuable component, coprecipitation can be intentionally utilized to recover it from a solution. Techniques like pre-treatment of the solution, adjusting pH, or adding masking agents can help minimize unwanted coprecipitation. In some cases, the coprecipitate is deliberately formed and then separated for analysis or recovery.